Roof racks for automobiles have been described and manufactured in a wide variety of designs, depending on the design of the particular roofs to which the racks are to be mounted, the means of mounting the rack to the roof, the shape and height of the crossbar, the method of clamping the crossbar (most often a separate piece) to the rack posts, and the degree to which the rack is adjustable for use on vehicles of different sizes. Critical to the design of all roof racks are an effective means of securing the rack to the roof in such a manner that it will not readily loosen when subjected to the jostling typically encountered as a result of the motion of the vehicle, particularly on rough roads. Much attention has also been directed to designing roof racks which are easy to assemble and secure to the vehicle roof. To this end, structures have been designed to provide for a single mechanism for clamping the crossbar to a support post or pedestal and the pedestal to the roof simultaneously. Examples of these may be found in Eklund, U.S. Pat. No. 4,496,089, Jan. 29, 1985; Thulin, U.S. Pat. No. 4,688,706, Aug. 25, 1987; and Prescott et al., U.S. Pat. No. 4,586,638, May 6, 1986.
The force vector which these mechanisms exert on the vehicle-clamping portion has vertical and horizontal components. The horizontal component holds the rack on the vehicle, and it can be very large without causing roof damage. The vertical component, on the other hand, is largely transverse to the roof surface.
Crossbars are generally of rigid, sturdy construction, permitting them to accommodate a large amount of clamping force without crimping. A high clamping force on the crossbar is frequently required to ensure against loosening, which not only disturbs the load being carried by the crossbar but also loosens the pedestal attachment to the vehicle. Typical automobile roofs, on the other hand, are made of thin sheet metal, and are not designed to support weight or excessive force. With many roof designs, there is a risk of denting the roof when tightening down one of these unitary mechanisms sufficiently to secure the crossbar to the pedestal, due to the vertical component of the force vector.
The problem is sometimes aggravated by the use of crossbars of different sizes. Industry standards require roof racks to be capable of accommodating all available crossbars within manufacturing tolerances. Most roof racks, however, are designed primarily for a certain size of crossbar. When crossbars of a size other than the design size are used, either larger or smaller, operators frequently try to compensate by tightening down the clamping mechanism even more, regardless of whether or not it is necessary to do so. The result is frequently a dent in the roof.
The present invention provides a vehicle roof rack structure which offers a number of advantages. The clamping of the crossbars to each of the pedestals is accomplished by cams facing inward, so that each cam exerts its clamping force by rotating in the direction toward the opposing pedestal, i.e., toward the center of the rack. In the event that vehicle jostling causes the cams to loosen and the pedestals to begin to move apart as a result, the crossbar will cause rotation of the cam due to friction at its contact surface to a tighter clamping position. This self-tightening of each of the cams acts as a check against loosening of the crossbar and disengagement of the entire structure from the vehicle roof. The construction disclosed herein also provides for independent clamping action of the crossbar to the pedestal on the one hand and the pedestal to the roof on the other, permitting the two clamping forces to be varied independently to meet their individual needs. Preferred embodiments of the invention include releasable limits or stops which lock the cams in their clamping position, further ensuring against inadvertent release due to jostling. In preferred embodiments, the engagement of these stops is achieved by the vehicle clamping mechanism, so that the cams are automatically locked in place upon securing the rack to the vehicle.
Further features, advantages and embodiments will be apparent from the following description.